The Holcombe Department of Electrical and Computer Engineering

Professor Michael Pursley receives grants for wireless communications research

Michael PursleyCLEMSON - ECE Holcombe Professor Michael Pursley has received a $345,000 grant from the Army Research Office for the study of Adaptive Reliable Unicast and Multicast Transmission in Tactical Packet Radio Networks.

The research in this project is devoted to new coding techniques and adaptive protocols that will meet future requirements for adaptive, reliable unicast and multicast transmission in tactical packet radio networks.  Such techniques and protocols provide reliable delivery of messages to a single destination or to multiple destinations simultaneously.  Pursley’s research group is seeking new protocols for adapting the modulation and coding that are used in these transmissions and for coordinating acknowledgments among the multiple destinations in a multicast network.  They also seek coding methods that will mitigate the effects of undelivered packets at some or all destinations. 

New application-layer coding techniques, referred to as fountain codes or rateless codes, are potentially very beneficial for multicast transmission in wireless networks, but they require adaptive transmission to make them suitable for the tactical communications environment.  Without physical-layer adaptation, application-layer coding is ineffective during long periods in which one or more links have deep fades or strong interference.  Pursley’s research group is employing a combination of analysis and simulation to gain an understanding of the interaction between application-layer coding, incremental-redundancy transmission, physical-layer coding, and the protocols for the adaptation of modulation and coding in multicast transmission systems. 

Pursley is also the recipient of a $300,000 grant from the Office of Naval Research for his research on Adaptive Multicarrier Transmission for Dynamic Spectrum Access in Tactical Cognitive Radio Networks with Fading Channels. A multicarrier signal consists of a set of carrier-modulated signals referred to as subcarriers.  Individual subcarriers can be included or excluded from the composite signal to match the availability of subcarrier frequency bands after accounting for the spectrum occupancy of other users.  By appropriate spacing of the subcarriers, multicarrier modulation formats, such as orthogonal frequency-division multiplexing (OFDM), provide frequency diversity to combat the fading and interference that are common obstacles to reliable communications in a tactical environment.

The goal of this research is to devise protocols that permit OFDM and related modulation formats to be used efficiently and reliably in tactical radio networks, thereby allowing dynamic access to the frequency spectrum. The research challenges are much greater for tactical applications than for typical commercial systems, because tactical radio networks lack the base stations, access points, and other forms of infrastructure that are employed in commercial networks.  Pursley’s research group is providing methods that enable the radios to derive information about the network and its communications links, and to then exploit the information for adaptation of the modulation and coding that are employed to transmit and receive packets.   To support this adaptive multicarrier transmission research, Pursley and his research group are also conducting basic research on new models that are suitable for the analysis and simulation of tactical communications over channels with time-varying propagation, fading, and interference.